1. Field of the Invention
The present invention relates to a liquid jet recording apparatus (an ink jet recording apparatus) and recover apparatus therefor, and more particularly to a liquid jet recording apparatus or the like capable of preventing the clogging of the recording head and effecting idle ink discharge (preliminary ink discharge) for removing the clogging in reasonable fashion.
2. Related Background Art
Ink jet recording apparatus for recording characters or images by dot matrix pattern by discharging recording liquid from a recording head onto a recording material such as paper or plastic sheet have the advantages of lower noises in operation in comparison with other recording apparatus, and of basically simple and inexpensive mechanical structure, and are widely employed as recording units for computers, word processors or the like.
In such ink jet recording apparatus, since the recording is achieved generally by discharging the recording liquid (ink) directly from a discharge port or opening (orifice) of the recording head, there is required particular consideration, unlike other recording apparatus, in order to maintain the recording head always in a state capable of ink discharge.
Since ink remains in the discharge port of the recording head even in the non-recording state, there is required means for preventing deterioration of ink in the discharge port such as drying of ink or increase of viscosity by evaporation, and, for this purpose there is already known an apparatus equipped with so-called capping means for preventing drying or evaporation of ink by covering the discharge port of the recording head with a cover in the non-recording state.
However, in low humidity condition or in between long periods of operation, the viscosity increase of ink cannot be prevented by the above-mentioned drying preventing means only, and there has been employed, in combination with said capping means, a discharge recovery mechanism for discharging the deteriorated ink from the discharge port The discharge recovery mechanism sucks the air from the cap covering the recording head thereby extracting ink from the discharge port by a negative pressure generated in said cap, or by pressurizes the discharge port for example with a pump.
However, such a recovery mechanism may still result in deterioration of ink in the discharge ports not used in the course of recording operation, since it is automatically activated for example at the start of power supply, and is not activated in the course of recording operation except for the case of a major discharge failure. In an apparat,us with plural discharge ports in the recording head, certain discharge ports are scarcely used according to the statistical nature of the data to be recorded, and the interval of ink discharge becomes very long in such discharge ports. Therefore, in discharge ports which are used only a limited number of times or have a long interval of ink discharge, the ink tends to exhibit viscosity increase resulting from drying, depending on the ambient conditions such as humidity or temperature, thus resulting in unstable ink discharge or absence of discharge.
In order to prevent such ink discharge failures, there is proposed so-called idle or preliminary ink discharge in which the recording head is brought to a non-recording position and the ink is discharged from the recording head.
In the conventional ink jet recording apparatus, said idle ink discharge operation is conducted on all the discharge ports at a predetermined constant interval. Consequently, the idle discharge is conducted even on properly operable discharge ports, thus increasing the ink consumption.
Such increased ink consumption limits the number of idle ink discharge operations, whereby the clogging is not completely removed, and certain discharge ports may therefore remain in a defective state.
Also the presence of such incomplete discharge ports cannot be detected, so that a recording operation in such state results in defects in the recorded image, such as a lack of recording or uneven density.